1. Field of the Invention
The present invention relates to a spin-valve type magnetoresistive head with the electric resistance changeable by the relationship between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer affected by the external magnetic field, in particular, to a spin-valve type magnetoresistive element capable of appropriately controlling the magnetization of a free magnetic layer without the need of providing a hard bias layer.
2. Description of the Related Art
FIG. 3 is a cross-sectional view showing a conventional configuration of a spin-valve type magnetoresistive element or a spin-valve type magnetoresistive head for detecting a recording magnetic field from a recording medium such as a hard disk.
As shown in the figure, an antiferromagnetic layer 1, a pinned magnetic layer 2, a non-magnetic electrically conductive layer 3, and a free magnetic layer 4 are formed, with hard bias layers 5, 5, provided at both ends thereof.
Conventionally, in general, the antiferromagnetic layer 1 comprises an Fexe2x80x94Mn (iron-manganese) alloy film or an Nixe2x80x94Mn (nickel-manganese) alloy film. The pinned magnetic layer 2 and the free magnetic layer 4 comprise an Fexe2x80x94Ni (iron-nickel) alloy film. The non-magnetic electrically conductive layer 3 comprises a Cu (copper) film. The hard bias layers 5, 5, comprise a Coxe2x80x94Pt (cobalt-platinum) alloy film. Numerals 6, 7 represent a base layer and a protection layer made from a non-magnetic material such as Ta (tantalum).
As shown in the figure, the antiferromagnetic layer 1 and the pinned magnetic layer 2 are formed adjacent to each other. The pinned magnetic layer 2 is in a single domain state in the Y direction by the exchange anisotropic magnetic field by the exchange coupling at the interface with the antiferromagnetic layer 1 so that the magnetization direction is fixed to the Y direction. The exchange anisotropic magnetic field is generated at the interface between the antiferromagnetic layer 1 and the pinned magnetic layer 2 by applying an annealing treatment (thermal treatment) while applying a magnetic field in the Y direction.
By the influence from the hard bias layers 5, 5, magnetized in the X direction, the magnetization direction of the free magnetic layer 4 is aligned in the X direction.
An antiferromagnetic material has the inherent blocking temperature. By exceeding the temperature, the exchange anisotropic magnetic field at the interface between the antiferromagnetic layer and the magnetic layer is vanished.
Therefore, the annealing treatment for putting the pinned magnetic layer 2 in a single domain state by the exchange anisotropic magnetic field at the interface between the antiferromagnetic layer 1 and the pinned magnetic layer 2 needs to be conducted at a temperature lower than the blocking temperature of the antiferromagnetic material comprising the antiferromagnetic layer 1. If a thermal treatment is applied at the blocking temperature or higher, the exchange anisotropic magnetic field is weakened (or vanished) so that the pinned magnetic layer 2 cannot be put in a single domain state in the Y direction to generate a problem of a large noise of the detection output.
The blocking temperature of an Fexe2x80x94Mn alloy film conventionally used as the antiferromagnetic layer 1 is about 150xc2x0 C., and the blocking temperature of an Nixe2x80x94Mn alloy film is about 400xc2x0 C.
The spin-valve type magnetoresistive element shown in FIG. 3 can be produced by forming 6 layers from the lower layer 6 to the protection layer 7, abrading out the side part of the 6 layers by an etching process such as an ion milling so as to have an inclined surface with an angle xcex8, and forming the hard bias layers 5, 5 at both ends of the 6 layers.
In the spin-valve type magnetoresistive element, a stationary current (detection current) is provided from electrically conductive layers 8, 8 formed on the hard bias layers 5, 5 to the pinned magnetic layer 2, the non-magnetic electrically conductive layer 3, and the free magnetic layer 4. The running direction of a recording medium such as a hard disk is the Z direction If the current is provided in the direction of the leakage magnetic field Y from the recording medium, the magnetization of the free magnetic layer 4 changes from the X direction to the Y direction The electric resistance is changed by the relationship between the change of the magnetization direction in the free magnetic layer 4 and the pinned magnetization direction in the pinned magnetic layer 2. The leakage magnetic field from the recording medium can be detected by the voltage change based on the electric resistance value change.
Since the spin-valve type magnetoresistive element shown in FIG. 2 has the hard bias layers 5, 5, at both sides of the 6 layers from the base layer 6 to the protection layer 7, the below-mentioned problems are involved.
The angle xcex8 of the inclined surface formed in the side part of the 6 layers from the base layer 6 to the protection layer 7 should be in an optional range. If the inclined surface is formed with an angle xcex8 outside the range, the leakage magnetic field from the hard bias layers 5, 5 in the X direction cannot be transmitted to the free magnetic layer 4 well so that it involves a problem in that the magnetization direction of the free magnetic layer 4 cannot be aligned completely in the X direction. Unless the magnetization direction of the free magnetic layer 4 is completely aligned in a single magnetic domain in the X direction, reproduction characteristics are affected such as generation of a Barkhausen noise.
Furthermore, in the spin-valve type magnetoresistive element shown in FIG. 3, the hard bias layers 5, 5 formed at both sides of the free magnetic layer 4 has a thin film thickness so that a sufficient bias magnetic field cannot be applied to the free magnetic layer 4 in the X direction. Therefore, it is disadvantageous in that the magnetization direction of the free magnetic layer 4 cannot be stable in the X direction, and thus a Barkhausen noise can be easily generated.
Moreover, the hard bias layers 5, 5 formed at both sides of the pinned magnetic layer 2 have a comparatively thick film thickness so that the pinned magnetic layer 2 receives a comparatively strong bias magnetic field from the hard bias layers 5, 5 in the X direction.
As heretofore mentioned, the magnetization of the pinned magnetic field 2 is fixed in the Y direction by the exchange anisotropic magnetic field at the interface with the antiferromagnetic layer 1, however, it may involve a problem in that the magnetization can be affected to change by the bias magnetic field from the hard bias layers 5, 5 in the X direction so that the leakage magnetic field from the recording medium cannot be detected well unless the magnetization of the pinned magnetic layer 2 is fixed firmly in the Y direction.
In order to solve the above-mentioned problems, an object of the present invention is to provide a spin-valve type magnetoresistive element comprising an antiferromagnetic layer (hereinafter referred to as a second antiferromagnetic layer) contacting with a free magnetic layer in place of a hard bias layer for aligning the magnetization direction of the free magnetic layer so as to align the magnetization direction of the free magnetic layer orthogonal to the magnetization direction of a pinned magnetic layer.
Another object of the present invention is to provide a production method of a spin-valve type magnetoresistive element capable of appropriately controlling the magnetization direction and the strength of a pinned magnetic layer and a free magnetic layer by selecting an antiferromagnetic material such that the blocking temperature of the second antiferromagnetic layer is lower than the blocking temperature of an ferromagnetic layer contacting with the pinned magnetic layer (hereinafter referred to as a first antiferromagnetic layer) and the exchange anisotropic magnetic field between the second antiferromagnetic layer and the free magnetic layer is smaller than the exchange anisotropic magnetic field between the first ferromagnetic layer and the pinned magnetic layer, and applying the annealing treatment utilizing the blocking temperature difference between the first ferromagnetic layer and the second ferromagnetic layer.
A spin-valve type magnetoresistive element of the present invention comprises a free magnetic layer and a pinned magnetic layer via a non-magnetic electrically conductive layer, a first antiferromagnetic layer contacting with the pinned magnetic layer for fixing the magnetization direction of the pinned magnetic layer by the exchange anisotropic magnetic field, and a second ferromagnetic layer contacting with the free magnetic layer for aligning the magnetization of the free magnetic layer orthogonal to the magnetization direction of the pinned magnetic layer by the exchange anisotropic magnetic field, wherein the first antiferromagnetic layer has a blocking temperature higher than that of the second antiferromagnetic layer, and the exchange anisotropic magnetic field between the first antiferromagnetic layer and the pinned magnetic layer is larger than the exchange anisotropic magnetic field between the second antiferromagnetic layer and the free magnetic layer.
According to the present invention, it is preferable that the blocking temperature of the first antiferromagnetic layer is 300xc2x0 C. or more, and the blocking temperature of the second antiferromagnetic layer is 100xc2x0 C. to 280xc2x0 C.
It is more preferable that the exchange anisotropic magnetic field between the first antiferromagnetic layer and the pinned magnetic layer is 200 Oe (oersted) or more, and the exchange anisotropic magnetic field between the second antiferromagnetic layer and the free magnetic layer is 2 to 200 Oe.
It is further preferable that the first antiferromagnetic layer is made from any of a Ptxe2x80x94Mn (platinum-manganese) alloy film, a Ptxe2x80x94Mnxe2x80x94X alloy (X represents at least one selected from the group consisting of Ni, Pd, Rh, Ir, Cr, and Co), or an Nixe2x80x94Mn (nickel-manganese) alloy film, and the second antiferromagnetic layer is made from any of an Irxe2x80x94Mn (iridium-manganese) alloy film, an Rhxe2x80x94Mn (rhodium-manganese) alloy film, an Fexe2x80x94Mn (iron-manganese) alloy film, or NiO (nickel oxide).
The above-mentioned Ptxe2x80x94Mn alloy film and Ptxe2x80x94Mnxe2x80x94X alloy film (X represents at least one selected from the group consisting of Ni, Pd, Rh, Ir, Cr, and Co) have a high blocking temperature of 300xc2x0 C. or more. Although it may depend on the film thickness of the pinned magnetic layer, in general, the exchange anisotropic magnetic field generated by the contact of these antiferromagnetic materials and the pinned magnetic layer is extremely large so that the magnetization of the pinned magnetic layer can firmly be in a single domain state. A large exchange anisotropic magnetic field can be obtained also by laminating these films above or below the pinned magnetic layer. Therefore, the Ptxe2x80x94Mn alloy film and Ptxe2x80x94Mnxe2x80x94X alloy film (X represents at least one selected from the group consisting of Ni, Pd, Rh, Ir, Cr, and Co) can be an appropriate material for the first antiferromagnetic layer.
When the first antiferromagnetic layer is made from a Ptxe2x80x94Mn alloy film, it is preferable that the composition ratio of the Ptxe2x80x94Mn alloy film is 44 to 51 atomic % of Pt and 49 to 56 atomic % of Mn. The exchange anisotropic magnetic field generated at the interface between the Ptxe2x80x94Mn alloy film with the composition ratio and the pinned magnetic layer is extremely large.
When the second antiferromagnetic layer is laminated above the free magnetic layer, the above-mentioned Irxe2x80x94Mn alloy film, Rhxe2x80x94Mn alloy film, and Fexe2x80x94Mn alloy film has a low blocking temperature of 280xc2x0 C. or less. Although it may partly depend on the film thickness of the free magnetic layer, the exchange anisotropic magnetic field generated at the interface between the antiferromagnetic materials and the free magnetic material is smaller with respect to the above-mentioned first antiferromagnetic material, therefore, the magnetization direction of the free magnetic layer can be aligned orthogonal to the magnetization direction of the pinned magnetic layer in a degree the magnetization can be reversed by an external magnetic field. When these materials are formed below the free magnetic layer, the exchange anisotropic magnetic field is extremely small compared with the case where these materials are formed above the free magnetic layer. Therefore, it is difficult to align the magnetization direction of the free magnetic layer. Accordingly, an Irxe2x80x94Mn alloy film, an Rhxe2x80x94Mn alloy film, and an Fexe2x80x94Mn alloy film are appropriate for the antiferromagnetic material when it is formed above the free magnetic layer. When the second antiferromagnetic layer is laminated below the free magnetic layer, the above-mentioned NiO film has a low blocking temperature of 280xc2x0 C. or less. Although it may partly depend on the film thickness of the free magnetic layer, the exchange anisotropic magnetic field generated at the interface between the antiferromagnetic material and the free magnetic material is small, therefore, the magnetization direction of the free magnetic layer can be aligned orthogonal to the magnetization direction of the pinned magnetic layer in a degree the magnetization can be reversed by an external magnetic field. When the NiO is formed above the free magnetic layer, the exchange anisotropic magnetic field is extremely small compared with the case where these materials are formed below the free magnetic layer. Therefore, it is difficult to align the magnetization direction of the free magnetic layer. Accordingly, NiO is appropriate for the second antiferromagnetic material when it is formed below the free magnetic layer.
A first aspect of a production method of a spin-valve type magnetoresistive element of the present invention comprises the steps of: laminating a first antiferromagnetic layer, a pinned magnetic layer, a non-magnetic electrically conductive layer, a free magnetic layer and a second antiferromagnetic layer, applying a thermal treatment at a temperature of ordering the crystal structure of the first antiferromagnetic layer or a temperature lower than the blocking temperature of the second antiferromagnetic layer while applying a magnetic field in the leakage magnetic field direction of a recording medium, and applying a thermal treatment at a temperature lower than the blocking temperature of the first antiferromagnetic layer but higher than the blocking temperature of the second ferromagnetic layer while applying a magnetic field in the direction orthogonal to the leakage magnetic field of the recording medium.
As mentioned above, in the present invention, the first antiferromagnetic layer and the second ferromagnetic layer need to satisfy the following conditions:
(1) The blocking temperature of the first antiferromagnetic layer is higher than the blocking temperature of the second ferromagnetic layer.
(2) The exchange anisotropic magnetic field between the first antiferromagnetic layer and the pinned magnetic layer is larger than the exchange anisotropic magnetic field between the second antiferromagnetic layer and the free magnetic layer.
An antiferromagnetic material satisfying the conditions are used as the first and second antiferromagnetic materials.
After laminating a first antiferromagnetic layer, a pinned magnetic layer, a non-magnetic electrically conductive layer, a free magnetic layer and a second antiferromagnetic layer, an annealing treatment is applied at a temperature of ordering the crystal structure of the first antiferromagnetic layer or a temperature lower than the blocking temperature of the second antiferromagnetic layer while applying a magnetic field in the leakage magnetic field direction of a recording medium as a first step. According to the step, the magnetization of both pinned magnetic layer and free magnetic layer can be aligned in the leakage magnetic field direction of the recording medium.
Then, as a second step, an annealing treatment is applied at a temperature lower than the blocking temperature of the first antiferromagnetic layer but higher than the blocking temperature of the second ferromagnetic layer while applying a magnetic field in the direction orthogonal to the leakage magnetic field of the recording medium. Since the annealing treatment is conducted at a temperature higher than the blocking temperature of the second antiferromagnetic layer, the exchange anisotropic magnetic field at the interface between the free magnetic layer and the second antiferromagnetic layer can be small (or vanished), the free magnetic layer in the single domain state in the direction the same as the magnetization of the pinned magnetic layer becomes a multi-domain state so as to have magnetic moments oriented in different directions in each magnetic domain. After achieving the state, by gradually lowering the temperature so as to have the annealing temperature lower than the blocking temperature of the second antiferromagnetic layer, the exchange anisotropic magnetic field is generated again at the interface between the second antiferromagnetic layer and the free magnetic layer and thus the magnetization direction of the free magnetic layer is aligned in the direction orthogonal to the magnetization direction of the pinned magnetic layer.
As mentioned above, since the exchange anisotropic magnetic field generated at the interface between the first anti ferromagnetic layer and the pinned magnetic layer is large, the magnetization of the pinned magnetic layer can be fixed firmly in the leakage magnetization direction of the recording medium. Further, since the exchange anisotropic magnetic field generated at the interface between the second antiferromagnetic layer and the free magnetic layer is small, the magnetization of the free magnetic layer can be aligned such that the magnetization can be reversed in the direction orthogonal to the magnetization direction of the pinned magnetic layer.
Accordingly since the magnetization of the free magnetic layer can be appropriately controlled in the present invention without the need of providing a hard bias layer as in the conventional embodiment, the multi-layer film comprising from the base layer 6 to the protection layer 7 needs not be formed in a trapezoid shape and thus the production process can be simplified.
Further, since the hard bias layer is not provided, the conventional problem of an unstable magnetization of the pinned magnetic layer caused by the effect from the leakage magnetic field of the hard bias layer to the pinned magnetic layer can be solved.
A second aspect of a production method of a spin-valve type magnetoresistive element of the present invention comprises the steps of: laminating a second antiferromagnetic layer, a free magnetic layer, a non-magnetic electrically conductive layer, a pinned magnetic layer and a first antiferromagnetic layer, applying a thermal treatment at a temperature of ordering the crystal structure of the first antiferromagnetic layer or a temperature lower than the blocking temperature of the second antiferromagnetic layer while applying a magnetic field in the leakage magnetic field direction of a recording medium, and applying a thermal treatment at a temperature lower than the blocking temperature of the first antiferromagnetic layer but higher than the blocking temperature of the second ferromagnetic layer while applying a magnetic field in the direction orthogonal to the leakage magnetic field of the recording medium. The function and effects the same as the above-mentioned first aspect can be achieved.